1. Field of the Invention
This invention relates to positive working precursors for masks and electronic parts and to methods of making such precursors using imagable compositions, and to masks and electronic parts made using such precursors. More particularly, this invention is directed to a thermal, positive working precursor for masks and electronic parts, wherein the precursor comprises a substrate having a layer comprising a film forming polymer which has at least one pendent IR-absorbing group, the layer is less soluble in a developer solution prior to exposure to IR radiation, and the layer is more soluble in the developer after exposure to IR radiation.
2. Background Information
WO 99/08879 describes certain thermally imagable compositions, and their use as imagable coatings on masks and on precursors for printed circuits and other electronic parts. They comprise polymeric materials admixed with compounds which inhibit the dissolution of the polymeric materials in a developer, that inhibition being removed by heat. Preferably the coatings include infra-red absorbing compounds, and the beat is produced by infra-red radiation, acting upon the infra-red absorbing compounds.
The technology described above is effective, but the need for a plurality of compounds has some implications for manufacturing and storage. Errors may occur in manufacturing, leading to products which are not optimal, or which are not wholly consistent, from batch to batch. After manufacture, there is a possibility that migration of separate components, for example the infra-red absorbing compounds, can occur. Furthermore often a substantial amount of infra-red absorbing compound is needed in order to absorb sufficient infra-red radiation to generate the heat to obtain good imaging, and those infra-red absorbing compounds, especially infra-red absorbing dyes, can be very expensive.
Accordingly, there remains a need for technological advances in relation to thermally imagable articles for use in mask and electronic part manufacture; and in particular there remains a need for articles which have a coating which is inexpensive to produce and is of good imaging forming characteristics.
The types of electronic parts whose manufacture may use an imagable coating include printed circuit wiring boards (PWBs), thick- and thin-film circuits, comprising passive elements such as resistors, capacitors and inductors; multichip devices (MDCs); integrated circuits (ICs); and active semiconductor devices. The electronic parts may suitably comprise conductors, for example copper board; semiconductors, for example silicon or germanium; and insulators, for example silica as a surface layer with silicon beneath, with the silica being selectively etched away to expose portions of the silicon beneath (a step in the manufacture of eg field effect transistors). In relation to masks, a required pattern may be formed in the coating on the mask precursor, which is then used as a mask in a later processing step, in forming a patter on, for example, a printing or electronic part substrate.
The present invention provides a positive working mask precursor or electronic part precursor having a layer including a film-forming polymer, on a substrate. The polymer of this invention has at least one pendent infra-red absorbing group. The layer initially has a first (i.e. lower) solubility prior to exposure to IR radiation. This first solubility is such that the layer does not readily dissolve in a developer liquid. However, when the layer is subjected to infra-red radiation, the layer acquires a second (i.e. higher) solubility, such that the layer more readily dissolves in the developer liquid compared to when the layer has the first solubility. In one preferred embodiment, the polymer has functional groups independently selected from xe2x80x94SONHR, xe2x80x94NHR, xe2x80x94SH and xe2x80x94OH, where R is H or a C1-C4 alkyl group, and the polymer additionally has pendent groups which absorb infra-red radiation, such as polymethine dye and cyanine dye residues. The polymer may be prepared by reacting a parent polymer with an infra-red absorbing compound.
The present invention also provides a method of making an electronic part or mask of this invention, by a method which comprises: (a) providing the above-described precursor; (b) via IR radiation, imagewise exposing areas of the thermally imagable layer carried by the substrate; and (c) contacting the precursor with a developer liquid to selectively remove the exposed areas of the layer.